1. Field of the Invention
The present invention relates generally to a method of and a system for controlling the air-fuel ratio of an air-fuel mixture produced for an internal combustion engine to a desired air-fuel ratio and particularly to a method and a system of this type in which the time required from provision of the air-fuel mixture to detection of a parameter representative of a function of the air-fuel ratio of the air-fuel mixture is reduced.
2. Description of the Prior Art
As is well known in the art, in a conventional air-fuel ratio control system, the air-fuel ratio of an air-fuel mixture produced for the engine has been controlled to a desired air-fuel ratio in accordance with a parameter representing an air-fuel ratio which has been sensed by a sensor located in the exhaust system of the engine.
Thus, the conventional air-fuel ratio control system has had a drawback that since an undesirably long time is required from production of an engine air-fuel mixture to detection of the air-fuel ratio of the air-fuel mixture due to the sensor being provided in the exhaust system, it is impossible to effectively control the air-fuel ratio of an engine air-fuel mixture to a desired air-fuel ratio.
As a solution to this problem, an air-fuel ratio control system has been proposed in which a part of an air-fuel mixture produced for an engine is extracted from the intake passageway thereof into a combustion gas generator, the extracted air-fuel mixture is burned in the combustion gas generator to form combustion gases therein, a sensor senses a parameter representative of a function of the concentration of a specific component in the combustion gases which concentration is closely related to the air-fuel ratio of the extracted air-fuel mixture, and the air-fuel ratio of an air-fuel mixture produced for the engine is controlled to a desired air-fuel ratio in accordance with the sensed parameter.
However, in this conventional air-fuel ratio control system, exhaust gases resulting from the combustion gases are conducted into the exhaust gas passageway of the engine. As a result, the conventional system requires measures for maintaining the pressure of the combustion gases at a tolerably high level. This is to make combustion of the extracted air-fuel mixture possible in spite of a high back pressure in the exhaust gas passageway and to at all times maintain stable combustion of the extracted air-fuel mixture without being influenced by variations in the pressure of engine exhaust gases in the exhaust gas passageway due to variations in engine load. Furthermore, when the extracted air-fuel mixture is not burned in the combustion gas generator due to a malfunction, or the like, the unburned air-fuel mixture is discharged to the atmosphere through the exhaust gas passageway to contaminate the atmosphere and at times the unburned air-fuel mixture causes an extraordinary combustion in the exhaust gas passageway to make the engine dangerous.